Analysis of the vasorelaxant action of jatrophone in the isolated aorta of the rat: influence of potassium channel blockers

Antinociceptive and anti-inflammatory activities of the Jatropha isabellei dichloromethane fraction and isolation and quantitative determination of jatrophone by UFLC-DAD

CONTEXT

Jatropha isabellei Müll. Arg. (Euphorbiaceae) has been used in the traditional medicine to treat arthritis.

OBJECTIVE

To evaluate the anti-inflammatory and antinociceptive activities of the dichloromethane fraction (DF_Ji) from underground parts of J. isabellei, and to develop an analytical method to quantify the diterpene jatrophone.

MATERIALS AND METHODS

Anti-inflammatory and antinociceptive activities of the DF_ji were determined by an acute arthritis model through assessment of the paw elevation time (PET) and articular diameter (AD) of Wistar rats treated orally (50, 100 or 200 mg/kg in a single-dose), and intravenously (0.1, 1, 10, 25 or 50 mg/kg in a bolus administration). The isolation of jatrophone from the DF_ji was carried out and confirmed by spectroscopic techniques. A UFLC-DAD method was developed and validated.

RESULTS

When orally administered, the highest dose (200 mg/kg) of DF_Ji was able to significantly reduce the PET to 24.8 ± 1.4 s (p < 0.01), when compared with the control group (33.7 ± 1.8 s). The administration of the intravenous dose of 10 mg/kg reduced the PET to 14.8 ± 0.3 s (p < 0.001). The oral and intravenous administration of the DF_Ji at dose of 200 and 10 mg/kg significantly prevented the formation of edema, reducing the AD in 25.3% and 32.5% (p < 0.01), respectively. The UFLC-DAD method allowed the quantification of jatrophone, which was found to be around 90 μg/mg of fraction.

DISCUSSION AND CONCLUSION

The DF_Ji displayed antinociceptive and antiedematogenic activities, representing a promising plant product for the arthritis treatment.

Vasodilator compounds derived from plants and their mechanisms of action

The present paper reviews vasodilator compounds isolated from plants that were reported in the past 22 years (1990 to 2012) and the different mechanisms of action involved in their vasodilator effects. The search for reports was conducted in a comprehensive manner, intending to encompass those metabolites with a vasodilator effect whose mechanism of action involved both vascular endothelium and arterial smooth muscle. The results obtained from our bibliographic search showed that over half of the isolated compounds have a mechanism of action involving the endothelium. Most of these bioactive metabolites cause vasodilation either by activating the nitric oxide/cGMP pathway or by blocking voltage-dependent calcium channels. Moreover, it was found that many compounds induced vasodilation by more than one mechanism. This review confirms that secondary metabolites, which include a significant group of compounds with extensive chemical diversity, are a valuable source of new pharmaceuticals useful for the treatment and prevention of cardiovascular diseases.

The ent-15α-Acetoxykaur-16-en-19-oic Acid Relaxes Rat Artery Mesenteric Superior via Endothelium-Dependent and Endothelium-Independent Mechanisms

The objective of the study was to investigate the mechanism of the relaxant activity of the ent-15α-acetoxykaur-16-en-19-oic acid (KA-acetoxy). In rat mesenteric artery rings, KA-acetoxy induced a concentration-dependent relaxation in vessels precontracted with phenylephrine. In the absence of endothelium, the vasorelaxation was significantly shifted to the right without reduction of the maximum effect. Endothelium-dependent relaxation was significantly attenuated by pretreatment with L-NAME, an inhibitor of the NO-synthase (NOS), indomethacin, an inhibitor of the cyclooxygenase, L-NAME + indomethacin, atropine, a nonselective antagonist of the muscarinic receptors, ODQ, selective inhibitor of the guanylyl cyclase enzyme, or hydroxocobalamin, a nitric oxide scavenger. The relaxation was completely reversed in the presence of L-NAME + 1 mM L-arginine or L-arginine, an NO precursor. Diterpene-induced relaxation was not affected by TEA, a nonselective inhibitor of K+ channels. The KA-acetoxy antagonized CaCl₂-induced contractions in a concentration-dependent manner and also inhibited an 80 mM KCl-induced contraction. The KA-acetoxy did not interfere with Ca²⁺ release from intracellular stores. The vasorelaxant induced by KA-acetoxy seems to involve the inhibition of the Ca²⁺ influx and also, at least in part, by endothelial muscarinic receptors activation, NO and PGI₂ release.

Cardiovascular properties of aqueous extract from Mitragyna inermis (wild)

Aqueous extracts of Mitragyna inermis (AEMI) used traditionally as antihypertensive agents produced a concentration-dependent (0.1-3 mg/ml) ex vivo increase in cardiac contractile response and coronary flow but did not modify heart rate in the rat. Interestingly, AEMI produced relaxation in isolated porcine coronary artery at concentration up to 3 mg/ml that was exclusively dependent on the presence of endothelium. This relaxation involved partial depolarization (KCl 20, 40 mM) and NO synthase inhibitor-sensitive mechanisms but was not sensitive to the blockade of cyclo-oxygenase pathway. In contrast, the relaxant effect of AEMI was not dependent on the presence of endothelium in rat tail artery. Taken together, the present study demonstrates hypotensive, cardiotropic and vasodilatory properties of AEMI that contribute to better understanding of its beneficial effect against cardiovascular diseases.

Analysis of the mechanisms underlying the vasorelaxant action of kaurenoic acid in the isolated rat aorta

The present work describes the mechanisms involved in the vasorelaxant effect of the diterpene ent-kaur-16-en-19-oic acid (kaurenoic acid). Kaurenoic acid (10, 50 and 100 microM) concentration-dependently inhibited phenylephrine and KCl-induced contraction in either endothelium-intact or -denuded rat aortic rings. Kaurenoic acid also reduced CaCl(2)-induced contraction in Ca(2+)-free solution containing KCl (30 mM). The diterpene did not interfere with Ca(2+) release from intracellular stores mediated by either phenylephrine (1 microM) or caffeine (30 mM). Kaurenoic acid (1-450 microM) concentration dependently relaxed phenylephrine-pre-contracted rings with intact (72.27+/-3.79%) or denuded endothelium (73.28+/-5.91%). The diterpene also relaxed KCl-pre-contracted rings with intact (80.44+/-3.68%) or denuded endothelium (78.12+/-1.26%). Pre-incubation of denuded aortic rings with N(G)-nitro-l-arginine methyl ester (l-NAME, 100 microM), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 1 microM) and 7-nitroindazole (100 microM) reduced kaurenoic acid-induced relaxation (percentage of relaxation: 49.12+/-3.26%, 53.10+/-6.72% and 51.74+/-4.76%, respectively). Indomethacin (10 microM) did not affect kaurenoic acid-induced relaxation. In endothelium-intact rings, 7-nitroindazole and N(pi)-nitro-l-arginine (l-NNA, 100 microM) displaced the curves for the diterpene to the right. Tetraethylammonium (5 mM), 4-amynopiridine (1 mM) and charybdotoxin (0.1 microM) caused a rightward displacement of the concentration-response curve for kaurenoic acid. Conversely, neither apamin (1 microM) nor glibenclamide (3 microM) affected kaurenoic acid-induced relaxation. Collectively, our results provide functional evidence that the effects elicited by kaurenoic acid involve extracellular Ca(2+) influx blocked. Its effects are also partly mediated by the activation of NO-cGMP pathway and the opening of K(+) channels sensitive to charybdotoxin and 4-amynopiridine. Additionally, the activation of the endothelial and neuronal NO synthase isoforms are required for the relaxant effect induced by kaurenoic acid.

Hypotensive and vasorelaxant effects of ethanolic extract from Jatropha gossypiifolia L. in rats

The present work was carried out to examine the hypotensive effects of ethanolic extract (EE) from Jatropha gossypiifolia L. The oral administration of EE (125 or 250 mg kg(-1) day(-1)) caused a significant and dose-dependent reduction of the systolic blood pressure. The concentration-response curves to norepinephrine (NE) or Ca(2+) were non-parallelly shifted to the right and the maximum contractile responses were concentration dependently depressed by EE (0.1 or 0.5 mg/ml) in endothelium-deprived mesenteric artery. The cumulative additions of EE (0.1-30 mg/ml) caused a concentration-dependent relaxant response in endothelium-deprived mesenteric artery precontracted with NE or Ca(2+). In conclusion, our results have shown that the EE from J. gossypiifolia L. can elicit hypotension, by oral via, in conscious normotensive rats and vasorelaxant activity on rat mesenteric rings precontracted with NE or Ca(2+).

Effects of Lepidium meyenii Walp and Jatropha macrantha on Blood Levels of Estradiol-17 .BETA., Progesterone, Testosterone and the Rate of Embryo Implantation in Mice

The effects of two Peruvian folk medicines, Lepidium meyenii Walp and Jatropha macrantha, on mouse sex steroid hormones and embryo implantation were investigated. Progesterone levels increased significantly in mice that received L. meyenii Walp, while testosterone levels increased significantly in mice that received L. meyenii Walp as well as in those that received both L. meyenii Walp and J. macrantha. However, there were no marked changes in blood levels of estradiol-17beta or the rate of embryo implantation.

Effects of the ethanolic extract of Spirulina maxima on endothelium dependent vasomotor responses of rat aortic rings

Dietary Spirulina decreases, endothelium-dependently, the responses to vasoconstrictor agonists and increases the endothelium-dependent, agonist-induced, vasodilator responses of rat aorta rings. The aim of this study was to analyze, in vitro, the effects of a raw ethanolic extract of Spirulina maxima on the vasomotor responses of rat aortic rings to phenylephrine and to carbachol. On rings with endothelium, the extract produced the following effects: (a) a concentration-dependent (60-1000 microg/ml) decrease of the contractile response to phenylephrine; (b) a rightward shift and a decrease in maximal developed tension, of the concentration--response curve to phenylephrine; (c) a concentration dependent relaxation of phenylephrine-precontracted rings. These effects were blocked by L-NAME, and not modified by indomethacin. The extract had no effect on the concentration-response curve to carbachol of rings with endothelium. On endothelium-denuded rings the extract caused a significant rightward shift of the concentration response curve to phenylephrine without any effect on maximal tension development. In the presence of the extract, indomethacin induced a marked decrease in the maximal phenylephrine-induced tension of endothelium-denuded rings. These results suggest that the extract increases the basal synthesis/release of NO by the endothelium and, also, the synthesis/release of a cyclooxygenase-dependent vasoconstricting prostanoid by vascular smooth muscle cells.

Compounds extracted from Phyllantus and Jatropha elliptica inhibit the binding of [3H]glutamate and [3H]GMP-PNP in rat cerebral cortex membrane

Glutamate is to be considered a nociceptive neurotransmitter and glutamatergic antagonists present antinoceptive activity. In this study we investigated the effects of the naturally occurring antinociceptive compounds rutin, geraniin and quercetine extracted from Phyllanthus, as well as the diterpene jatrophone, extracted from Jatropha elliptica on the binding of [3H]glutamate and [3H]GMP-PNP [a GTP analogue which binds to extracellular site(s), modulating the glutamatergic transmission] in rat brain membrane. Jatrophone inhibited [3H]glutamate binding and geraniin inhibited [3H]GMP-PNP binding. Quercetine inhibited the binding of both ligands. These results may indicate a neurochemical parameter possibly related to the antinoceptive activity of these natural compounds.

Analysis of rabbit vascular responses to DBI, an ingol derivative isolated from Euphorbia canariensis

We have analysed the effects of 7,12-O-diacetyl-8-O-benzoil-2,3-diepiingol (DBI), an ingol derivative isolated from E. canariensis, on isometric tension developed by isolated rabbit basilar and carotid arteries. Concentration-response curves to DBI (10(-8) - 3 x 10(-5) M) were obtained cumulatively in both arteries at resting tension and active tone (KCI, 50 mM). At resting tension, DBI induced a concentration-dependent contraction, which was not inhibited in Ca(2+)-free medium. H7 (1-(5-isoquinoline sulphonyl)-2-methylpiperazine dichloride) (10(-4) M) inhibited the DBI-induced contraction both in basilar and in carotid arteries. Calmidazolium (10(-4) M) inhibited the maximum contraction of the carotid artery to DBI, and completely abolished the response in the basilar artery. In pre-contracted basilar arteries DBI induced a concentration-dependent relaxation that was not modified by incubation with NG-nitro-L-arginine (L-NOARG; 10(-5) M) or indomethacin (10(-5) M). In the carotid artery with active tone DBI induced further contractions, which were not significantly modified by L-NOARG (10(-5) M) and were potentiated by indomethacin (10(-5) M). These results suggest that DBI contracts rabbit basilar and carotid arteries by a mechanism that is independent of extracellular Ca2+ and involves the participation both of protein kinase C and of calmodulin. DBI relaxes basilar but not carotid arteries by a mechanism independent of the liberation of nitric oxide and prostacyclin. In the carotid artery prostacyclin but not nitric oxide partially counteracts the contractile action of DBI.

Jatrophone and 12-O-tetradecanoyl phorbol-13-acetate antagonism of stimulation of natural killer activity and lymphocyte proliferation

We have recently reported that the diterpene jatrophone antagonizes the effects of phorbol ester in pharmacogical studies. In order to investigate further whether this action is associated with an inhibition of protein kinase C activity, we examined the effect of jatrophone on the stimulation of lymphocyte activities which are dependent on the protein kinase C pathway. Jatrophone (0.02-0.32 microM) caused concentration-dependent and equipotent inhibition of human lymphocyte proliferation induced by 5 micrograms/ml of phytohemagglutinin or by a combination of 100 ng/ml of 12-O-tetradecanoyl phorbol-13-acetate (TPA) plus 0.15 microM ionomicyn, with IC50 values (and their 95% confidence limits) of 53.4 (42.6-65.3) nM and 48.4 (39.4-59.8) nM, respectively. Jatrophone also blocked, in a concentration-dependent fashion, the murine lymphocyte proliferation stimulated by 5 micrograms/ml of concanavalin A, with an IC50 value of 63.5 (51.2-76.5) nM. The inhibition was not due to a toxic effect as the pre-incubation of lymphocytes for 48 h with 0.32 microM jatrophone did not impair the proliferation after removal of the diterpene from the culture medium. Human lymphocytes when pre-treated with 10 ng/ml TPA had a 3 times higher spontaneous natural killer activity against K562 cells and an increased expression of CD69. In addition, jatrophone inhibited both spontaneous and TPA-stimulated natural killer activity and the expression of CD69. Jatrophone concentrations that inhibited 75% of lymphocyte proliferation did not impair the intracellular increase in Ca2+ flux in lymphocytes stimulated by phytohemagglutinin. These results indicate that jatrophone is a potent inhibitor of activation of lymphocytes, probably through inhibition of the protein kinase C pathway.

Cardiac and vascular responses of isolated rat tissues treated with diterpenes from Sinularia flexibilis (coelenterata: octocorallia)

The marine environment is a rich source of compounds with cardiovascular activity. This study characterizes the cardiac and vascular responses in isolated rat tissues of flexibilide, dihydroflexibilide and sinulariolide, three diterpenes isolated from the soft coral Sinularia flexibilis. On rat left ventricular papillary muscles, dihydroflexibilide and flexibilide showed similar potencies (-log EC50 = 4.69 +/- 0.05 and 4.66 +/- 0.06, respectively); the maximal response to dihydroflexibilide of 1.4 +/- 0.2 mN was 35 +/- 7% that of calcium chloride in the same muscles. All diterpenes relaxed rat thoracic aortic rings precontracted with KC1 (100 mM) with similar potencies (flexibilide, -log EC50 = 4.17 +/- 0.06). Flexibilide was further characterized and shown to increase force in isolated rat left atria by 0.8 +/- 0.5 mN at 1 x 10(-4) M, to increase rate of contraction in isolated rat right atria by 18 +/- 5 beta/min at 3 x 10(-5) M and to completely relax endothelium-denuded rat thoracic aortic rings (-log EC50 = 4.14 +/- 0.05). Toxicity as indicated by the occurrence of ectopic beats was not observed with the diterpenes at concentrations which produced complete relaxation of blood vessels, maximal positive inotropic activity and minor positive chronotropic responses. Thus, these compounds may be useful lead compounds in the search for improved treatment of cardiovascular disease, especially heart failure.

The relaxant action of jatrophone in rat portal vein. A comparison with protein kinase C inhibitors

Jatrophone, staurosporine and H-7, caused graded inhibition of rat portal vein contractions induced by phorbol 12-myristate 13-acetate (PMA), noradrenaline, endothelin-1 or KCl, with IC50s of 86 nM, 13 microM, 11 microM and 9 microM, respectively. Jatrophone was equipotent to H-7, but 100 to 500 fold less potent than staurosporine. Jatrophone, H-7 and staurosporine, also dose-dependently inhibited rhythmic contractions of the rat portal-mesenteric vein with IC50s of 15 microM, 9 microM and 75 nM, respectively. Jatrophone, H-7 and staurosporine caused graded relaxations of preparations contracted with endothelin-1 or PMA with IC50s of 12 and > 1000 microM, 8 and 13 microM and 7 and 12 nM, respectively. All three compounds caused graded inhibition of caffeine-induced contractions in Ca(2+)-free solution containing EGTA. The similarity between the vasorelaxant actions of jatrophone, staurosporine and H-7 in rat portal vein suggests that jatrophone acts, at least in part, through inhibition of PKC-dependent mechanisms. Moreover, like the PKC inhibitors, its vasorelaxant action may also involve other mechanisms unrelated to protein kinase C inhibition.